LuLu is the free, shared-source firewall for macOS. Its goal is simple; block any unknown outgoing connections, until approved by the user. While it was designed to generically detect malware by flagging unauthorized networking connections, LuLu can also be used to block OS components or 3rd-party applications from transmitting information to remote servers. What's to like about LuLu? Lots! 100% free As in no ads, no time trials, no missing features.